Sorry for the late reply -- for some reason I did not get a notification for this post and I only just saw it.
I am afraid the creation of a helper instance is integral to the way Byteman operates. The helper carries the rule trigger context which is unique to each specific triggering of the rule.
I am not sure why you are worried about GC costs. Normally helper instances only exist across the lifetime of the rule triggering (i.e. while the rule is being executed). In most cases that means they are allocated and die in the Eden GC space. This normally causes no significant memory overhead and merely implies that young GC collections happen with a very small increase in frequency.
Do you have any measurements to suggest that GC costs are significantly increased because of Helper instance creation? Are you retaining handles on Helper instances across rule triggerings? I'd be happy to look into any problems you have found if you can provide me further details to see if I can advise on ways to avoid them.